Tracking bovine beasts to help birds
Nest trampling and ground nesting birds: Quantifying temporal and spatial overlap between cattle activity and breeding redshank. Sharps, E., Smart, J., Mason, L.R., Jones, K., Skov, M.W., Garbutt, A. & Hiddink, J.G. 2017. Ecology and Evolution. DOI: 10.1002/ece3.3271. VIEW
Saltmarsh grazing is important for breeding Redshank, Tringa totanus, but the livestock introduced to graze the marshes have been called ‘bigfoot’ due to their clumsiness around fragile nests, which causes a sticky situation for the feathered occupants. In this tale of Redshank breeding until the cows come home, we tracked cattle to ask: what is the crunch point?
Figure 1 Redshank, Tringa totanus © Kevin Simmonds
Advances in technology means it’s now easier than ever to record animal movements, and studies have placed GPS trackers on everything from gannets to gazelles. This has helped to improve our understanding of these species, which in turn has helped conservationists understand how to manage habitats. In our quest to find out what causes high rates of Redshank nest trampling, we fitted GPS collars to cattle grazing the saltmarshes where the Redshank nest.
Back in 2011, I was one of a team of fieldworkers who had the good fortune of spending two months doing RSPB surveys of breeding Redshank on saltmarshes. I traveled around various marshes in North-west England, whilst other fieldworkers covered different parts of the UK. Using these data, a paper published by Lucy Mason showed that Redshank populations on British saltmarshes had declined by >50% since 1985 (Malpas et al. 2013). The following year, I started my PhD looking at nest survival of Redshank breeding on saltmarshes. We found that although Redshank selected nests in grazed vegetation (Sharps et al. 2016), grazing negatively affected Redshank nest survival. This occurred both directly through trampling of nests, and indirectly by causing Redshank to nest in shorter vegetation where they had increased nest predation (Sharps et al. 2016, 2015). Whilst carrying out these two years of fieldwork, we had noticed that the cattle hardly ever seemed to spread out across the whole marsh, and instead stayed at the landward edges of the marshes close to the sea wall where many of the Redshanks were. Could this be causing high rates of nest trampling?
Figure 2 Cattle on a saltmarsh © Adam Cross
To understand these issues, we fitted GPS collars onto livestock. These were fitted to cattle on four saltmarshes in the Wash Estuary in Eastern England, and this two-year study (2013 and 2014) is the subject of our paper recently published in Ecology and Evolution. Cattle only used between 3% and 42% of the saltmarsh extent and spent most of their time on the higher elevation habitat within 500m of the sea wall, moving further onto the saltmarsh as the season progressed. It’s these higher elevation zones where Redshank, and (to a lesser extent) other bird species such as Skylark, Alauda arvensis, and Oystercatcher, Haematopus ostralegus, typically nest and this breeding coincides with the early period of grazing.
Figure 3 Trampled Redshank egg © Christine Tansey
As part of this study, we also placed dummy nests onto one of the marshes. These were actually clay pigeon shooting targets, which have a similar diameter to Redshank nests, and like eggs break when trampled by cattle. We placed these ‘nests’ in 30 plots, with 9 disks in each plot which enabled us to calculate trampling probability at different points on the saltmarsh. We found that this probability of nest trampling was correlated to the livestock density we recorded using the GPS loggers and was up to six times higher in the areas where Redshank breed. This overlap in both space and time of the habitat use of cattle and Redshank means that the trampling probability of a nest can be much higher than would be expected based on standard measures of cattle density.
Figure 4 A trampled dummy nest © Elwyn Sharps
When some people hear this, they say “well why don’t we just stop grazing saltmarshes?”, but things aren’t that simple and that’s unlikely to help Redshank. These birds are more abundant on grazed saltmarshes (Norris et al. 1998) and grazing produces the tufts of grassy vegetation that Redshank need for nesting (Sharps et al. 2016, Mandema et al. 2014). Instead we suggest that habitat managers aim to keep livestock away from Redshank nesting habitat between mid-April and mid-July. This could be achieved through delaying the onset of grazing, or introducing a rotational grazing system. Getting the balance right will require fine tuning, and we need to be careful that changes in site management that reduce nest trampling don’t end up making the saltmarshes less suitable for Redshank. This could happen if the new grazing regime caused changes to the habitats – too much tall vegetation may prevent Redshank from nesting or provide hiding places for predators (Laidlaw et al. 2015), whilst not enough tall vegetation can leave nests more exposed and easier for predators to find (Sharps et al. 2016, 2015).
Figure 5 Animation of cattle movements and Redshank nesting habitat: Purple = preferred Redshank breeding habitat, Grey = habitat not normally used for Redshank nesting. The different coloured dots represent GPS points from each logger © Jan Hiddink
To make sure any changes in saltmarsh grazing are positive for Redshank, the RSPB and Natural England are working together to carry out trial management. Lead by Jen Smart, Lucy Mason and colleagues in the RSPB Centre for Conservation Science this work will be carried out on saltmarshes across England. Their main aim will be to discover how grazing management can reduce the negative effects of nest trampling, whilst still maintaining valuable saltmarsh grazing for livestock managers, and producing the correct habitat for Redshank and other saltmarsh birds.
References and further reading
Appleton, G. 2016. Big Foot and the Redshank Nest. Wader Tales, April 4, 2016. Available from: https://wadertales.wordpress.com/2016/04/04/big-foot-and-the-redshank-nest/. VIEW
Laidlaw, R.A., Smart, J., Smart, M.A. & Gill, J.A. 2015. The influence of landscape features on nest predation rates of grassland-breeding waders. Ibis 157(4): 700-712. VIEW
Malpas, L.R., Smart, J., Drewitt, A., Sharps, E. & Garbutt, A. 2013. Continued declines of Redshank Tringa totanus breeding on saltmarsh in Great Britain: is there a solution to this conservation problem? Bird Study 60: 1-14. VIEW
Mandema, F.S., Tinbergen, J.M., Ens, B.J. & Bakker, J.P. 2014. Spatial diversity in canopy height at Redshank and Oystercatcher nest-sites in relation to livestock grazing. Ardea 101: 105-112. VIEW
Norris, K., Brindley, E., Cook, T., Babbs, S., Brown, C.F. & Yaxley, R. 1998. Is the density of redshank Tringa totanus nesting on saltmarshes in Great Britain declining due to changes in grazing management? Journal of Applied Ecology 35: 621-634. VIEW
Sharps, E., Garbutt, A., Hiddink, J.G., Smart, J. & Skov, M.W. 2016. Light grazing of saltmarshes increases the availability of nest sites for Common Redshank Tringa totanus, but reduces their quality. Agriculture, Ecosystems & Environment 221: 71-78. VIEW
Sharps, E., Smart, J., Skov, M.W., Garbutt, A. & Hiddink, J.G. 2015. Light grazing of saltmarshes is a direct and indirect cause of nest failure in Common Redshank Tringa totanus. Ibis 157(2): 239–249. VIEW
Featured image: Redshank, Tringa totanus © Kevin Simmonds
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